This invention relates generally to papermaking fabrics and more particularly to dual layer weaves that are typically used as forming fabrics in papermaking and related machines. Such fabrics, when used in the forming step of the papermaking process, receive the slurry of the cellulosic fibers and form extended webs of the paper as moisture is withdrawn by vacuum boxes beneath the fabric drawing out the water. Accordingly, a desirable feature for such fabrics is high air permeability, a feature that may be enhanced by a dual layer weave. Papermaking fabrics having dual layer weaves include two layers of yarns extending in the cross machine direction interwoven with a single set of machine direction yarns. The respective yarns of the two cross direction layers generally are stacked with a yarn of one layer being directly above a corresponding yarn of the other layer or set. Thus, there are generally about an equal number of cross direction yarns in each layer.
Papermaking fabrics conventionally are woven either flat or endless. A flat woven fabric is woven in a single sheet with the warp yarns extending in the machine direction and the weft yarns extending in the cross machine direction. After weaving is completed the opposed ends of the warp filaments, and thus of the fabric sheets, are joined together to form a continuous belt. Endless woven fabrics are woven with the weft yarns extending in the machine direction and the warp yarns extending in the cross machine direction, with the fabric being woven as an endless loop that may not require any seam.
A goal of such papermaking fabrics has always been to increase the durability and wear resistance of the fabric. Another goal has been to improve the air permeability to facilitate faster removal of water to thus speed the formation of paper on the fabric. Increased wear resistance is one of the benefits of a dual layer fabric, particularly one in which the cross direction yarns on the machine side have long floats under a number of machine direction yarns. However, where improved wear resistance has been achieved with such a weave, there frequently has been a less than desired air permeability for removal of water.